Janet Arey, Ph.D., and Roger Atkinson, Ph.D., Air Pollution Research Center, University of California, Riverside

Overview

It has been hypothesized that much of the high morbidity and mortality associated with fine particulate matter is due to quinones, such as 9,10-phenanthrenequinone, which have the ability to form reactive oxygen species (ROS) and cause oxidative stress. During this experimental program, we used the facilities and expertise available at the Air Pollution Research Center, University of California, Riverside, to investigate atmospheric reactions of alkylnaphthalenes and phenanthrene and to assess their potential to contribute to the ambient PAH-quinone burden.

Based on our measured yields, calculations suggest that daytime OH radical-initiated and nighttime NO3 radical-initiated reactions of gas-phase phenanthrene will be significant sources of 9,10-phenanthrene-quinone in ambient atmospheres. In contrast, the ozone reaction with phenanthrene is unlikely to contribute significantly to ambient 9,10-phenanthrenequinone. The high yield (>30%) of 9,10-phenanthrenequinone from the NO3 radical-initiated reaction implies the potential for high concentrations of this quionone to be formed in areas where nighttime NO3 radical chemistry is important, such as Southern California.Hydroxyl radical-initiated reactions of naphthalene, naphthalene-d8, 1- and 2-methylnaphthalene (1- and 2-MN), 1- and 2-ethylnaphthalene (1- and 2-EN) and the 10 isomeric dimethylnaphthalenes (DMNs) were conducted in a large volume Teflon chamber with analysis by atmospheric pressure ionization - mass spectrometry (API-MS).

Quinone products were very minor, but the major products were ring-opened dicarbonyls that are 32 mass units higher in molecular weight than the parent compound, one or more ring-opened dicarbonyls of lower molecular weight resulting from loss of two -carbons and associated alkyl groups, and ring-containing compounds that may be epoxides. The isomer-specific identifications and, importantly, the genotoxicity of these novel oxygenated species should be determined as well as their presence in ambient atmospheres. Gas-phase NO3 radical-initiated reactions of naphthalene, the MNs, ENs and DMNs were conducted, and for the first time, the dimethylnitronaphthalene and ethylnitronaphthalene isomers formed were identified and their yields measured.

Radical-initiated reactions of a mixture of ENs/DMNs proportioned to mimic ambient concentrations gave profiles of the ENNs and DMNNs expected to be formed from OH and NO3 radical-initiated reactions. Comparing these ENN/DMNN profiles with those from ambient samples collected in Mexico City, Mexico, Riverside, and Redlands, California, it is apparent that the nitro-PAH formation in Mexico City was dominated by OH radical reaction, while the ENN/DMNN profiles from Southern California could only be explained by the occurrence of nighttime NO3 radical chemistry. This research suggests that nighttime NO3 chemistry can be a significant source of toxic nitro-PAHs and PAH-quinones in ambient atmospheres.

Speaker Biography

Janet Arey, Ph.D., has been at the Air Pollution Research Center at the University of California, Riverside since 1982 and has been a faculty member in the Department of Environmental Sciences and the Interdepartmental Graduate Program in Environmental Toxicology at UCR since 1990. Dr. Arey is the author or co-author of over 150 publications dealing with the atmospheric chemistry of organic compounds.

Roger Atkinson, Ph.D., is a Research Chemist at the Air Pollution Research Center and a Professor in the Department of Environmental Sciences and the Department of Chemistry at UCR . Dr. Atkinson is the author or co-author of over 300 technical publications dealing with the atmospheric chemistry of volatile organic compounds.